The present invention relates to a magnetic bubble propagation device. It is applicable to the circulation of binary information or bits, materialized in the form of separated magnetic domains, called bubbles in a bubble store. These domains have an opposite magnetization to that of the remainder of the magnetic material constituting the layer in which they are formed.
It is known that in a magnetic bubble store, each bubble can be displaced by a force. This movement can take place freely in any random direction in the plane of the magnetic layer. The magnetic layer is a magnetic garnet and the bubbles are formed in said layer by applying a d.c. magnetic field thereto perpendicular to the plane of the layer. This field is produced in practice by a permanent magnet and also ensures the non-volatility of the information contained in the store. The magnetic garnet in which the bubbles are formed is generally supported by an amagnetic monocrystalline garnet.
It is known to displace the bubbles by applying a rotary magnetic field, which is difficult to realise and whose function is to create poles, e.g. on permalloy patterns, which are in the form of T-bars, chevrons or semi-disks. In this way, shift registers are produced in which the binary information is represented by the presence 1 or the absence 0 of a bubble. Apart from these permalloy patterns, it is known that it is necessary to use electrical conductors for producing on the bubble store chip, writing, information recording, non-destructive reading, register-to-register transfer and erase functions. Erasing is carried out bit-by-bit by selective destruction of the bubbles, or in an overall total manner. This erasure can be obtained simply by increasing the value of the d.c. magnetic field to beyond the maximum value permitted for recording.
It is also known that a large number of known bubble stores have a magnetic garnet layer in which is effected an ion implantation around patterns corresponding to non-implanted zones of said garnet layer. As a result of their shape, these patterns constitute shift registers along which the bubbles cancirculate in the implanted zone. The magnetic bubbles are formed in the garnet layer, in the implanted portion thereof, on the peripheries of the non-implanted patterns. These patterns generally have an elongated shape and the reading or transfer of the content of the registers generally takes place by circulating the bubbles occurring at their ends towards another register or towards a reading station. This circulation of the bubbles at the ends of the registers is generally ensured by conductive sheets superimposed on the magnetic garnet layer at the ends of the registers and representing windows. These sheets are traversed by pulse-type currents supplying the bubbles which have reached the ends of the registers, either to another register, or to the reading station. This circulation is obtained by the appearance of positive and negative poles on the edges of the windows at the time when a current pulse is applied to the corresponding conductive sheet. Generally, these windows are arranged parallel to one another and perpendicular to a line corresponding to the direction along which the bubbles must travel. The passage of each bubble from the edge of one window to the edge of another window takes place in the magnetic garnet layer by attraction of said bubble as a result of appropriate polarities of the edges of the windows. This type of bubble circulation at the ends of registers of a bubble store is, for example, described in French patent application No. 8,008,765 on Apr. 18, 1980 in the name of the same Applicant.
A bubble store is also known in which the propagation of the bubbles is ensured by means of a device incorporating an electrically conductive sheet having windows, associated with non-implanted islands of the magnetic garnet layer. This type of propagation is described in the article by A. H. BOBECK entitled "Current access magnetic bubble circuits", Bell Laboratories, 600 Mountain Avenue, Murray Hill, N.J. "Bell System Technical Journal", Vol. 58, No. 6, July 1979.
In this type of propagation, as in that described in the aforementioned patent application, the magnetic bubbles are attached to or engaged on the border of the non-implanted island in the implanted region. During their displacements by a vertical field produced by a current in the sheet, the bubbles have to overcome the potential barrier at the border of said non-implanted patterns. A unidirectional, static plane field of 2100 Oersted (Oe) is applied in order to eliminate the "hard" bubbles. These hard bubbles are in fact bubbles having a reduced mobility and which have difficulty in following the direction imposed by the field.
A magnetic bubble store is also known in which the bubbles are propagated by a device incorporating an electrically conductive field having windows, as well as non-implanted patterns in the form of disks, of the magnetic garnet layer. This device is described in the article by H. OHTA entitled "Current Access Ion-Implanted Bubble Device Structure" corresponding to the lecture given by the author on Mar. 3, 1981 at the Atlanta International Conference on Magnetism and Magnetic Materials. In this type of device, when the ion implantation conditions are appropriate, there are charged walls at the edge of a non-implanted disk. The bubbles are propagated with the aid of vertical magnetic fields, which are produced by the charged walls linked with these patterns and by a hole in a current sheet. A rotary current applied to the sheet permits the displacement of the bubbles.
The propagation devices which use rotary fields are difficult to realise. The known devices using conductive sheets with windows associated with non-implanted islands and which use a vertical displacement field and a plane field for eliminating the hard bubbles, as well as the device using vertical fields and rotary currents, require a high power level for each propagation of an information bit.